Application of a critical wedge taper model to the Tertiary transpressional fold-thrust belt on Spitsbergen, Svalbard

The Tertiary opening of the North Atlantic Ocean involved major and long-li ved overall dextral transpression between the Svalbard and Greenland plates . On Spitsbergen, this tectonic event is manifest as a 100-200-km-wide cont ractional fold-thrust belt in the form of an east-pinching prism. This belt can be subdivided into (1) a western, basement-involved hinterland provinc e that reveals more complex deformation, including thrust, transcurrent, an d normal faulting, and (2) an eastern thin-skinned fold-thrust belt with st ructures oriented subparallel (north-north west-south-southeast) to the tra nsform plate boundary. The time-space distribution and interaction of different structural styles of Tertiary deformation evident on Spitsbergen support a model with Linked, long-term and short-term (episodic) dynamic growth of a composite contract ional and transcurrent fold-thrust wedge. The growth of a narrow, high-tape r (critical-supercritical) contractional wedge occurred during northward-di rected crustal shortening (stage 1) in an oblique, dextral transcurrent set ting. Crustal thickening in the form of thrust uplift and basin inversion a nd strike-slip duplexing during the main contractional event (stages 2 and 3) created an unstable, supercritical wedge of basement and cover rocks in the hinterland. At the same time, a broader and more homogeneous frontal pa rt of the wedge developed eastward by in-sequence imbrication in order to r educe the taper angle. Local erosion and lateral wedge extrusion (stages 3 and 4) modified the oversteepened hinterland wedge to a critical taper angl e. Continued tectonic activity in the hinterland caused renewed internal im brication of the frontal wedge, where deformation was accommodated by tear faulting and out-of-sequence thrusting (stage 4). Adjustment toward a stabl e taper geometry included local extension (stage 5) and erosion and sedimen tation. In a transpressional fold-thrust belt, as on Spitsbergen, out-of-plane (oro gen oblique to parallel) transport in the hinterland may cause local and la teral supercritical and subcritical wedge tapers. Hinterland geometries cou ld trigger adjustments in a frontal thrust wedge in a decoupled situation, and/or orogen oblique or parallel motions in a coupled situation. Changing kinematics may thus be expected along strike in such an orogen.